In August 2021, in a soil crater, the latest Mars pirate digs into one of its first rocks.
The drill bit attached to the arm of the Perseverance pirate swept away the dust, and on top of it lay a few millimeters of rocky millstone in a 5-centimeter circle. From just above, one of the hacker’s cameras was taken, which are fixed together like broken shells. The presence of interlocking crystal tissues became evident. Those textures were not what most of the scholars who had spent years preparing for the mission thought.
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Then the scientists watched in a video interview as two pirated spectrometers revealed the chemistry of tissue networks. The visible figures together with the chemical compositions showed that this rock, according to Rochette, was volcanic in origin. Not from clay and silt, which was once found in the bed of a lake.
Nicknamed Percy, the pirate arrived at the Jezero crater two years ago, on February 18, 2021, with his helicopter sidekick, Ingenuity. The most complex spacecraft to explore the Martian surface, Percy builds on the work of the pirate Curiosity, which has been on Mars since 2012, the twin explorers Spirit and Opportunity, the Pirate Crusader and other destroyers.
But the purpose of perseverance is different. While the previous wanderers are focused on Martian geology and looking at the idea of a planet, Percy is looking for signs of past life. Jezero was chosen for the March 2020 mission because it appears from orbit to be a pristine lake environment where microbes could thrive, and its large Delta would preserve any traces of them. By drilling, scraping and collecting pieces of the Red Planet, the pirate uses his seven science tools to analyze the bits for any hint of ancient life. He also collects samples to return to Earth.
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Once in port, “we were able to start the story of what happened in the lake, and it’s pretty complex,” said Briony Horgan, a planetary scientist at Purdue University in West Lafayette, Ind., who helps plan Percy’s day-to-day and long-term operations.
The millstone was just one of the traps the pirate discovered. Hundreds of researchers have analyzed the persistence of data and now only have some idea of how the crater has evolved over time. This basin saw a lava flow, at least one lake that lasted for perhaps ten thousand years, rivers that created silty sand deltas, and heavy floods that brought rocks from far away.
Jezero has a more dynamic past than scholars have predicted. That volatility slowed down the search for sedimentary rocks, but it also revealed new chambers where ancient life could have taken hold.
Persistence inverts the carbonaceous material — the basis of life on Earth — in every example, Horgan says. “They see us everywhere.” And he still has more to explore.
Perseverance found unexpected rocks
The Jezero Crater is a small crater about 45 kilometers in diameter, north of the planet’s equator. The crater formed sometime between 3.7 billion and 4.1 billion years ago, the first billion years in the solar system. It sits on an older and much larger rock known as Isis. In the western bend of the Jezero, an ancient channel gives way to the dry, ventilated crater floor of the delta.
That delta “is like these twinkling glasses that are pretty visible from orbit that tell us we’re standing here as a body of water,” says astrobiologist Ken Williford of Blue Marble Space Science in Seattle.
Perseverance landed in a crater area about two kilometers from the front of the Delta. Physicists thought they would find layers of earth and sand there, at the base of what they called Lake Jezero. But the landscape immediately looked different than expected, says planetary geologist Kathryn Stack Morgan of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. Stack Morgan is deputy policy scientist for persistence.
In the first few months after landing, the Mars 2020 mission team tested the movements and instruments, slowly, carefully. But from the first real science drilling near the harbor site, researchers on Earth realized what they had found. The texture of the rock, says Stack Morgan, “was the texture of an igneous rock.” It looked like a lava flow.
Over the next six months, more rocks were exposed on the crater floor of the igneous texture. Some exciting rocks, including Rochette, show olivine crystals throughout. “The crystal structure was obviously cooled from the melt, not transported grains,” which would be the case if it were a sedimentary sample, Abigail Allwood of the Jet Propulsion Lab. She leads PIXL, a hacking tool that uses X-rays to identify the composition of each sample.
Astronomers now believe that the crater was filled only by two separate igneous rocks — both after the crater was created, and between 3.7 billion and 4.1 billion years ago. In one, magma was pushed from the planet’s interior to the surface, cooled and solidified, and then exposed by erosion. In the other, a smaller wash flowed on the surface.
Sometime after these events, water flowed from nearby mountains into the crater to form a lake ten meters high and at least ten thousand years old, according to some groups of members. Percy’s tools showed the ways in which water had changed igneous rocks: for example, scientists found sulfates and other minerals that require water to form, and they saw empty pits inside cracks in the rocks where water washed away the material. As the water flowed down into the lake like rivers, it deposited silt and mud, forming deltas. The flood released 1.5-meter-wide rocks from that distance. All of these events preceded the Lake Drought, which may have occurred about 3 billion years ago.
The Core samples, which Perseverance collects on board and adjusts for the event’s return to Earth, could provide the dates when the igneous rocks formed, as well as when the Martian surface dried. During the intervening period, Lake Jezero and other wet environments were stable enough for microbial life to begin and survive.
“Fixing the geologic time scale is critical to understanding Mars as a habitable world,” Stack Morgan says. “And we can’t do that without up-to-date models.”
About a year after landing on Mars, Perseverance rolled several kilometers across the crater floor to the front of the Delta – where it encountered very different geology.
The delta would hold signs of ancient life
Standing as a symbol of the deity, the perennial bodies of water — stable localities that could sustain life. Plus, it grows over time, traps and preserves organic matter.
Sand and silt deposited where the river hits the lake is layered with sedimentary material, building the Delta fan. “If any biological material gets caught in that sediment, it gets buried very quickly,” says Martian geologist Eva Scheller of MIT, a researcher with Percy’s team. “This creates an environment that is very good for preserving organic matter.”
While exploring the delta front between April 2022 and December 2022, Perseverance found some of the sedimentary rocks behind it.
Some of the hacking tools focused on the textures and shapes of the rocks, while other tools gathered more detailed spectral information, revealing the elements that were in those rocks. By combining the data, researchers can piece together what rocks are becoming and what processes might be changing in SSS. It is this chemistry that could reveal signs of ancient Martian life – biosignatures. Scientists are still in the early stages of these analyses.
There won’t be a single life-threatening sign, Allwood says. But the pirate will show more of a “character drive” with slowly building evidence that life was once there.
The chemical characteristics suggestive of life are most likely to hide in the sedimentary rocks, as he studied persistence in the front of the delta. Particularly interesting are the extremely fine silt rocks. Such sediments are silt, Horgan says, where — in deltas of the earth, at least — organic matter is concentrated. So far, though, the pirate hasn’t found those murky materials.
But studying sedimentary rocks revealed unexpected carbonates, sulfates, and salts—all materials that interact with water and are important to life as we know it. Percy found carbon-based material scraped off every rock, Horgan says.
“We’ve had some really interesting results that we’re pretty excited about as a community,” Horgan says of the delta front exploration. Some of them may be announced in March at the Lunar and Planetary Science Conference.
Persistence leaves examples for future mission
Perseverance, as at the beginning of February, collected 18 samples, including Martian debris and buckets of rock, on board and stored them in sealed boxes for the eventual return to Earth. Samples from the crater floor, the delta front rocks, and the Martian atmosphere are also thin.
In the last weeks of 2012 and the first weeks of 2013, the pirate released — or rather carefully — half of the collected samples, as well as a tube that indicated whether the samples contained any terrestrial contaminants. The captured troops of Mars are now seated in front of the Delta, in a pre-determined place called the three Caudinas.
If Perseverance does not perform well enough to deliver its samples on the shuttles when the future sample return energy arrives, the mission will collect these samples from the drop site to return to Earth.
Researchers are currently working on plans for a joint Mars mission between NASA and the European Space Agency that could retrieve samples. Launching in the late 2020s, Persistence would be a pirate soon. Percy would transfer samples to launch a small rocket from Mars and return to Earth in the 2030s. Lab tests could then confirm what persistence has already been discovered and discover much more.
Meanwhile, Percy ascends the Delta to explore its summit, where the turbid sedimentary rocks are still to be found. The next attack is the edge of the former lake, where the shallow water has stood for a long time. This is the site Williford is most excited about. Much of what we know about the history of life on Earth comes from an environment with thin water, he says. “Where it’s really rich, they start to form underwater ecosystems,” he says. “There’s not much chemistry going on there.”
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